CDC: Early Estimates on the Effectiveness of This Year's Flu Vaccine

A new report by the Centers for Disease Control and Prevention (CDC) suggests that the 2014–15 influenza vaccine has low effectiveness against circulating influenza A (H3N2) viruses, but vaccination is still recommended.

Since 2004–2005, the CDC has estimated the efficacy of seasonal influenza vaccine in the prevention of medically attended acute respiratory illness (ARI) associated with laboratory-confirmed influenza. The CDC evaluated data from 2,321 adults and children enrolled in the U.S. Influenza Vaccine Effectiveness Network (Flu VE) during November 10, 2014 to January 2, 2015 across study sites in Michigan, Pennsylvania, Texas, Washington, and Wisconsin. Analysis showed that during this period, overall VE was 23% (95% CI: 8–36%). Of the total patients with ARI enrolled, 41% tested positive for influenza virus, 96% of which were identified as influenza A, and 4% as influenza B.

Compared with previous seasons, this season's interim VE estimate is relatively low. This suggests that over two-thirds of circulating H3N2 viruses are antigenically and genetically drifted from the H3N2 vaccine component of 2014-2015. Northern Hemisphere seasonal influenza vaccines. By January 3, 2015, forty-six states reported widespread flu activity, with most infections caused by the influenza A (H3N2) viruses.

The CDC is still recommending the influenza vaccination in patients aged 6 months and older because it can still prevent some infections with the circulating H3N2 viruses as well as other viruses that might appear later in the season, such as the influenza B viruses. Vaccines with a reduced VE can still prevent influenza-related complications, including hospitalizations and death. In addition, antiviral use is recommended as adjunct to vaccination especially given the reduced vaccine efficacy. A neuraminidase inhibitor should be administered to all patients at high risk for serious influenza complications within 48 hours of symptom onset if influenza is suspected.

The CDC report also included techniques to help reduce the spread of influenza: respiratory hygiene, cough etiquette, social distancing, and hand washing.